The present embodiments relate to electronic devices and are more particularly directed to a compass for use in an electronic device, where the compass is operable irrespective of the magnetic field in which the device is located.
Electronic devices are extremely prevalent and beneficial in today's society and are constantly being improved due to consumer and user demand. One technological example has been the portable or cellular telephone marketplace, which has seen great advances in the last many years. These devices have evolved beyond provision of voice services alone and are now accommodating greater amounts of data and are providing various additional features, more advanced operating systems, and additional programming. For example, so-called “smart phones” are envisioned as having a large impact on upcoming generations of cellular phones. Also, various personal digital assistants (“PDAs”) are still succeeding in the marketplace and may do so for the foreseeable future. Further, the functionality of cellular phones and PDAs are now beginning to overlap with the possibility of a greater combination of the functionality of these devices into a single unit in the future.
With the advancement of the devices introduced above, various newer features are now being developed and implemented, as are known in the art. One feature that is now found in some cellular phones is a magnetically-responsive compass. As a compass, the device serves in the ordinary sense of such a component, that is, to present to the phone user an indication of the directionality of the physical orientation of the phone. In the present art, such a compass is constructed in part using an element (or elements) that is sensitive to the local magnetic field, that is, the field at the location of the phone. For example, one implementation uses a two-dimensional magneto-resistive measurement bridge, which changes its resistance in response to a change in the orientation of the bridge as influenced by the local magnetic field. Circuitry, such as a differential amplifier and an analog-to-digital converter, sense the voltage output of the bridge and translate that output into a corresponding directionality indication.
While the preceding approach to a cellular phone compass may prove a desirable feature in some instances, the present inventor has observed that it has certain drawbacks. For example, the magneto-resistive measurement bridge extends only in two dimensions, presumably to coincide with the two-dimensional nature of the circuit board(s) inside the phone. As such, the bridge might produce erroneous and indeed erratic indications if the phone is positioned in a manner that is not parallel to the earth's surface. As another example, because the bridge is responsive to local magnetic field, then the resulting output will produce an erroneous indication of direction when the phone is in a location that is subject to aberrations in the earth's magnetic filed or nearby metal objects that might distort the earth's magnetic field at the then-existing location of the phone. As still another example, both device cost and circuit board space are increased with the inclusion of the bridge circuit and its associated circuitry.
As a result of the preceding, there arises a need to address the drawbacks of the prior art as is achieved by the preferred embodiments described below.